1. Field of the Invention
The present invention relates to a photoelectric smoke sensor having a light emitting device and light receiving device for detecting light scattered by smoke particles, and a fire detecting system including a plurality of the sensor, and more particularly to a sensitivity test of a photoelectric smoke sensor.
2. Description of the Related Art
FIG. 7 shows a general photoelectric smoke detector, in which a smoke detection chamber 2 is formed by a plurality of labyrinth members 1 so that light does not enter from the outside but smoke flows in from outside. A light emitting surface of a light emitting device (LED) 3 and a light receiving surface of a light receiving device 4 are arranged in the smoke detection chamber 2 so that light emitted from the light emitting device 3 is not directly received but scattered light 6 due to smoke particles 5 can be received by the light receiving device 4. Further, a light emitting surface of a light emitting device 7 for testing is arranged in the smoke detection chamber 2 in face-to-face relation to the light receiving surface of the light receiving device 4 so as to produce pseudo-scattered light. Further, operation confirmation device 8 is provided so as to project to the outside of this smoke sensor.
In such an arrangement, as shown in FIG. 8(a), if there are no smoke particles 5 in the smoke detection chamber 2, an output V of the light receiving device 4 is based only on the diffusively reflected light from the labyrinth member 1 and the like as well as dark current. Accordingly, the output V remains at the lowest level. The voltage of the output in this condition is so-called 0-point level voltage. As smoke flows into the smoke detection chamber 2 and the quantity of scattered light 6 (that is, smoke density D) increases due to the smoke particles 5, the output V becomes proportionally higher. Accordingly, an arrangement can be provided such that in an initial state in which the interior of the smoke detection chamber 2 has not been fouled, an alarm signal is outputted to a control panel (not shown) when the output of the light receiving device 4 exceeds a threshold value Vmin. corresponding to a threshold value Dmin. of the smoke density which is the minimum value of the allowable range of the sensitivity of the sensor, as shown by the solid line in FIG. 8(a).
In addition, when a test is conducted by using the light emitting device 7 for testing, it is possible to carry out an operation test for confirming the operation of the sensor by causing the light emitting device 3 for smoke detection to emit light, and by causing the light emitting device 7 for testing to emit light at an operational level corresponding to a smoke density Dt which is greater than or equal to the aforementioned threshold value Dmin.
When the interior of the smoke detection chamber 2 becomes fouled, the overall output V of the light receiving device 4 becomes high, as shown by the broken line in FIG. 8(a), and even if the smoke density is less than or equal to the threshold value Dmin., the output V of the light receiving device 4 becomes greater than or equal to the threshold value Vmin., thereby outputting an alarm signal.
Accordingly, it is necessary to conduct a non-operation test in this type sensor in addition to the above-mentioned operation test. For example, as shown in FIG. 8(b), an operation test value Dt of the smoke density is set to be slightly smaller than the maximum value Dmax. of the allowable range Dw of sensitivity. The light emitting device 7 emits light at a level corresponding to the value Dt to conduct the operation test in order to confirm the operation of the sensor. In addition, a non-operation test value Df is set to be slightly smaller than the minimum value Dmin. of the allowable range Dw of sensitivity. The light emitting device 7 emits light at a level corresponding to the value Df to conduct the non-operation test in order to confirm the non-operation of the sensor.
At the operation test value Dr, since the output voltage Vt1 and Vt2 corresponding to the initial sensitivity characteristic and the sensitivity deviation characteristic respectively, exceed a alarm output minimum level Vmin., the operation of the sensor can be confirmed at both output voltage. On the other hand, at the non-operation test value Dr, the output voltage Vf1 corresponding to the initial sensitivity characteristic does not exceed the alarm output minimum level Vmin., whereby the non-operation test can be conducted. However, since the output voltage Vf2 corresponding to the sensitivity deviation characteristic exceeds the alarm output minimum level Vmin., the non-operation test can not be conducted.
For example, the operation and non-operation test of the sensor are conducted in a manner as shown in FIG. 9. In a smoke sensor 106 which is mounted on a ceiling, a reed switch for operation 105 and a reed switch for non-operation 104 is provided diagonally. An inspector 101 brings a test pole 102 to come near the smoke sensor 106. First, the inspector 101 moves the test pole 102 so that a magnet 103 come near the reed switch for operation to conduct the operation test. Second, the inspector 101 moves the test pole 102 to rotate in the direction of an arrow in the drawing so that the magnet 103 come near the reed switch for non-operation to conduct the non-operation test.
However, when the non-operation test is conducted at or below the operational level, a setting must be provided such that the quantity of light emitted by the light emitting device 7 for testing is slightly lower than at the operational level, as shown in FIG. 8(b). However, there is a problem in that it is difficult to provide an accurate setting such that the quantity of light emitted by the light emitting device 7 for testing is slightly lower than at the operational level, because of the diffusively reflecting structure in the smoke detection chamber 2 and variations in circuit components.
In addition, variable resistors are required to adjust separately the level in order to accurately set this level, resulting in higher cost. Furthermore, since two test operations are carried out including the operation test and the non-operation test, there is a problem in that much time is required when tests are conducted on each of a multiplicity of sensors installed in a large monitoring area.
Moreover, as another conventional testing method, a conceivable method is that output terminals, such as a connector and a jack, are provided in advance for directly fetching the output V of the light receiving device 4 to an external circuit, and the output V (the so-called 0-point level) when smoke is not present in the smoke detection chamber 2 is measured. With this method, however, output terminals and a measuring instrument are required, and the inspector must engage in an operation at high places where the sensors are installed. Additionally, since output terminals for testing and openings therefor have to be provided separately, there is a problem in that the sensors are affected by external noise such as electromagnetic waves, corrosion, aged deterioration, and the like.